The objective of this research is to elucidate the biochemical mechanisms underlying the stimulation of hepatic glycogenolysis by gamma-adrenergic agents. Preliminary data indicate that epinephrine acts predominantly through gamma-receptors to activate glycogenolysis in rat liver and that Beta-receptors and cyclic AMP play minor roles. It is proposed to study the molecular basis of the gamma-adrenergic stimulation of hepatic glucose output using isolated liver cells and phenylephrine as the principal test system. Phosphorylase, glycogen synthetase and protein kinase activities will be measured to determine whether activation or inactivation of these enzymes is involved. Assays for synthetase phosphatase, phosphorylase kinase and phosphorylase phosphatase will be developed if data indicate the involvement of these enzymes. Cyclic AMP and cyclic GMP will be assayed to obtain further evidence of the non-involvement of cyclic AMP and to examine the possible involvement of cyclic GMP. The possible role of changes in intracellular free Ca ions will be examined by varying the external Ca ions concentration and by using agents which block or facilitate the movement of Ca ions across membranes. If none of the above experiments identifies the intracellular mediator of gamma-adrenergic action, a search for such an agent will be carried out.